JP2000269918A - Orthogonal frequency division multiplex transmission system and transmitter and receiver using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain with a simple method an OFDM transmission system effectively utilize frequencies by fully suppressing the spectrum components of a signal out-band. SOLUTION: A power revision device 10 receives each subcarrier whose signal point is arranged by a mapping device 2, so as to form a shape of frequency spectrums with subcarrier power whose gradient is gradually decreased as the power is separated from a center frequency in the area of a signal band is away from the center frequency by a prescribed frequency width or over, so that frequencies are utilized effectively with a simple method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an orthogonal frequency division multiplexing (OFDM) transmission system in which each subcarrier is modulated, which is used for wireless communication, and a transmission device and a reception device using the same.

[0002]

2. Description of the Related Art Conventionally, when an OFDM signal is wirelessly transmitted, it is necessary to sufficiently suppress a spectrum outside a signal band so as not to adversely affect an adjacent radio frequency channel. It was suppressed by a filter. When using a band-pass filter, it is difficult to make the center frequency variable, so in order to transmit on a desired radio frequency channel, after up-converting the band-pass filter output, a low-pass filter or a high-pass It is necessary to suppress the image frequency by a pass filter or the like, which has a disadvantage that the circuit scale is large.

There is also known a method of suppressing the spectrum outside the signal band by making use of the characteristics of the OFDM signal and making the subcarrier at the end of the signal band slower in transmission speed than the subcarrier near the center. . However, when the guard time is generated by changing the transmission speed of the subcarrier, it is impossible to use the guard time insertion method as performed in the normal OFDM method.
That is, the normal guard time insertion method uses a method of copying the rear part of the symbol after the inverse discrete Fourier transform to the beginning of the symbol, but in the case of a method of changing the transmission speed of the subcarrier, Inverse discrete Fourier transform is separately performed for subcarriers with low transmission speed, and additional processing of adding to the guard time generated only with subcarriers with high transmission speed is required, which increases the circuit scale. Would.

[0004] A conventional transmitting device and a conventional receiving device will be briefly described below.

FIG. 18 shows the structure of a conventional OFDM transmitting / receiving apparatus. In the transmitting device, the serial data to be transmitted is converted into parallel data by the S / P converter 1, and then the mapping for linear modulation is performed by the mapper 2. An inverse discrete Fourier transformer (IDFT) 3 following the subsequent stage performs an inverse discrete Fourier transform, and the guard inserter 4 copies the part after the symbol to the beginning of the symbol. Subsequently, after quadrature modulation by the quadrature modulator 5, the spectrum outside the signal band is suppressed by a band-pass filter (BPF) 6 having a constant center frequency.

Thereafter, the signal is up-converted by an up-converter 7 to match the frequency of a radio frequency channel to be transmitted, passes through a low-pass filter 8 to remove an image, and is radiated from an antenna 9 to a radio transmission line. Is done.

[0007] In the receiving device, a component other than a desired band in the signal received by the antenna 11 is converted to a bandpass filter 1.
2 and input to the subsequent quadrature demodulator 13. A low-pass filter 14 is used downstream of the quadrature demodulator 13 to remove an image generated by the quadrature demodulator. Conventionally, since this low-pass filter 14 is for removing an image, it does not have the characteristic of amplifying it within the signal band.

Next, after the digital signal is converted into a digital signal by the A / D converter 15, the guard section inserted on the transmission side is removed by the guard remover 16, and then the frequency domain is removed by the discrete Fourier transformer (DFT) 17. Is converted to a signal. Next, after demodulation by the demapper 18 corresponding to the mapping on the transmitting side, the P / S converter 19
Thus, the receiving data is output.

[0009]

In the case of wireless transmission of a signal of the OFDM transmission system, the conventional system and apparatus require a complicated circuit as described above, and the circuit scale becomes large. However, in order to use limited frequencies effectively, it is desirable to sufficiently suppress spectral components outside the signal band by a simple method.

An object of the present invention is to realize an OFDM transmission system capable of effectively utilizing a frequency by sufficiently suppressing a spectral component outside a signal band by a simple method, and a transmission device and a reception device using the same. And

[0011]

SUMMARY OF THE INVENTION In order to solve this problem, the present invention provides a method for reducing the subcarrier power gradually as the distance from the center frequency increases in a signal band within a region separated from the center frequency by a certain frequency width or more. This is an orthogonal frequency division multiplex transmission system using a communication signal in which a frequency spectrum shape is formed so as to have such a gradient.

Further, a transmission apparatus using such an orthogonal frequency division multiplex transmission system is configured.

Further, a receiving apparatus using such an orthogonal frequency division multiplexing transmission system is constituted.

Thus, the spectrum outside the signal band can be reduced by a simple method, and the frequency can be used effectively.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention according to claim 1 of the present invention provides a communication system using an orthogonal frequency division multiplexing (OFDM) transmission system in which each subcarrier is modulated. In a region separated by a frequency width or more, orthogonal frequency division multiplexing characterized by using a communication signal whose frequency spectrum shape is formed so as to have a gradient such that subcarrier power gradually decreases as the distance from the center frequency increases. This is a transmission method and has an effect that frequencies can be effectively used by a simple method.

According to a second aspect of the present invention, there is provided a power changing means for gradually reducing the subcarrier power in a region apart from the center frequency by a certain frequency width or more in the signal band as the distance from the center frequency increases. A transmitting apparatus using the orthogonal frequency division multiplexing transmission method according to claim 1, which has an effect that a frequency can be effectively used with a simple configuration.

According to a third aspect of the present invention, in the signal band, the subcarrier power in a region away from the center frequency by a certain frequency width or more is gradually increased as the distance from the center frequency is increased, and the frequency region outside the signal band is increased. 2. A receiving apparatus using an orthogonal frequency division multiplexing transmission system according to claim 1, further comprising a band selecting / amplifying means having a filter function for removing a signal of the subcarrier.
The dynamic range of the subsequent discrete Fourier transformer or the like can be improved without changing N (carrier power to noise ratio), and the frequency can be effectively used with a simple configuration.

According to a fourth aspect of the present invention, in the orthogonal frequency division multiplexing transmission system according to the first aspect, the communication signal is formed by subcarriers selected according to importance. By constructing a spectrum with subcarriers corresponding to degrees, a flexible transmission system can be constructed.

[0019] In particular, as in the invention according to claim 5, the communication signal is formed by arranging in a frequency spectrum region that is farther away from the center frequency as the subcarrier determined to be less important. According to the orthogonal frequency division multiplexing transmission method of claim 4, a signal of high importance is transmitted near the center of a signal band of high subcarrier power, and a signal of low importance is transmitted in a signal band of low subcarrier power. The transmission at the end has an effect that transmission quality according to the importance of the signal can be ensured.

According to a sixth aspect of the present invention, there is provided the orthogonal frequency division multiplexing transmission system according to the fourth or fifth aspect, wherein the communication signal includes transmission line frequency characteristic information. This has the effect that a more reliable transmission system that follows changes can be constructed.

According to a seventh aspect of the present invention, using the orthogonal frequency division multiplexing transmission method according to the fourth or fifth aspect, transmission data and content information are input, and the importance of each subcarrier is determined to determine the importance information. , And an importance consideration S / P for inputting the transmission data and the importance information, selecting a subcarrier based on the importance information, and performing serial / parallel (S / P) conversion. The transmitting device according to claim 2, further comprising a P conversion unit.
By configuring a spectrum with subcarriers according to importance, it has an effect that a transmission device for constructing a flexible transmission system can be formed.

According to an eighth aspect of the present invention, transmission data and content information are input, the importance of each subcarrier is determined, and importance information is output using the orthogonal frequency division multiplexing transmission method of the sixth aspect. Inputting the transmission data, the importance information, and the transmission path frequency characteristic information, and selecting a subcarrier based on the importance information and the transmission path frequency characteristic information to perform serial / parallel operation. (S /
3. The transmission apparatus according to claim 2, further comprising: (P) an S / P conversion unit considering importance, which performs conversion, wherein a power changer changes the subcarrier power based on the transmission path frequency characteristic information. In addition, even in a transmission path condition such as frequency-selective fading, there is an effect that a more reliable transmission apparatus that can follow a change in the frequency characteristic of the transmission path can be formed.

According to a ninth aspect of the present invention, a numerically controlled oscillator (NCO) for inputting a timing signal and a subcarrier and outputting in-phase component and quadrature component subcarrier power according to the subcarrier is provided for each subcarrier. A power changer for changing the power value of the sub-carrier power of the in-phase component and the quadrature component; a first adder for adding the power value of the changed in-phase component; and a power value of the quadrature component after the change. 3. The transmitting apparatus according to claim 2, further comprising: a second adder for performing quadrature modulation by inputting an output of the first adder and an output of the second adder. ,
This has the effect that the spectrum outside the signal band can be suppressed while accurately satisfying the orthogonal condition between subcarriers.

According to a tenth aspect of the present invention, in the numerical control oscillator, the phase step generator outputs a phase step value such that the phase changes gradually and continuously, and the phase step generator outputs the phase step value. 10. The transmission device according to claim 9, further comprising: an accumulator for adding a spectrum to the signal.

According to the present invention, there is provided a variable coefficient setting device for generating a variable coefficient based on a timing signal, and a multiplier for multiplying the output of the numerically controlled oscillator by the variable coefficient. 11. The transmission device according to claim 9, wherein the variable coefficient setting device is controlled so as to amplify or attenuate gently with time, and that an out-of-band spectrum can be suppressed with a simple configuration. Having.

According to a twelfth aspect of the present invention, in the numerical control oscillator, the address control means for determining an address value corresponding to the subcarrier is shared by all the numerical control oscillators corresponding to the number of subcarriers, and 12. A transmission device according to claim 9, further comprising a storage unit that selects and outputs a value based on the storage unit, and shares a storage unit having a large circuit scale, such as a look-up table. This has the effect of reducing the size of the transmission device.

According to a thirteenth aspect of the present invention, the numerically controlled oscillator includes an address determining means for determining an address value corresponding to the subcarrier, and all the numerically controlled oscillators shared by all the subcarriers. And an address match detecting means for determining whether there is a match and outputting a judgment value, and when the judgment value includes coincidence information, shifts the address value by a necessary amount and outputs the result. 12. The transmission apparatus according to claim 9, further comprising: an address shift unit that outputs an address value as it is, and a storage unit that selects and outputs a value based on the address value from the address shift unit. In addition, the shared storage means such as a look-up table can be used efficiently, and the peak power can be reduced.

According to a fourteenth aspect of the present invention, the storage means comprises:
A ROM storing output values associated with the input; and control means for inputting all address values, extracting corresponding values from the ROM based on each, and outputting the values in parallel. Item 12. The transmission device according to Item 12 or 13, which has an effect that a shared ROM such as a look-up table can be efficiently used, and an easy circuit design is possible.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG.

(Embodiment 1) FIG. 1 is a block diagram showing a configuration of a transmitting apparatus according to the present embodiment. In FIG. 1, 1 is an S / P converter, 2 is a mapper, and 3 is an IDF.
T unit, 4 is a guard inserter, 5 is a quadrature modulator, 8 is LP
F and 9 are transmitting antennas, which perform the same operations as those of the transmitting device shown in FIG.

The transmitting apparatus of FIG. 1 includes a power changer 10 which is a means for reducing the subcarrier power at the end of the signal band near the center of the signal band, after the mapping unit 2 in the conventional transmitting apparatus of FIG. It is arranged.

The operation of the transmitting apparatus shown in FIG. 1 is as follows. The input digital data is input to the S / P converter 1 to perform serial / parallel conversion, and the mapping unit 2 performs signal point arrangement for modulation. At 10, the subcarrier power at the end of the signal band is made smaller than that near the center. And IDFT
The parallel signal is inverse Fourier-transformed by the modulator 3 to output a complex signal, and the guard inserter 4 copies the latter part of the complex signal symbol after the inverse discrete Fourier transform to the head of the symbol, and then outputs the quadrature modulator 5 , Orthogonally modulates the complex signal in which the guard interval is inserted, removes an image generated by the orthogonal modulation by the LPF 8, and radiates an electromagnetic wave as a transmission signal from the transmission antenna 9 to the wireless transmission path.

The specific operation of the power changer 2 will be described below. FIG. 2 is a schematic diagram showing a frequency spectrum of an input signal to the power changer 2, and FIG. 3 is a schematic diagram showing a frequency spectrum of an output signal from the power changer. Here, N indicates the number of subcarriers, and fs indicates a subcarrier frequency interval.

The input signal has a spectrum of a uniform level within the signal band as shown in FIG. 2, but at the time of output, as shown in FIG. 3, the signal greatly affects the frequency spectrum outside the band. A signal in which the power of the signal at the end of the band is reduced is output.

As an example of a specific configuration of the power changer 2, for example, a correlation table of an output with respect to an input is provided, and an operation is performed such that a signal corresponding to the level of an input signal is selected and output. Power conversion can be performed.

With the means for converting power, the level of the frequency spectrum outside the band can be suppressed, so that effective frequency utilization can be easily realized.

Note that the power changer determines in advance that the quadrature-modulated signal has a smaller subcarrier power at the end than near the center of the band, so that the parallel signal input to the inverse discrete Fourier transformer is set in advance. Among them, since it is a means for converting the power although it affects the power of the signal after quadrature modulation, it is also possible to provide this function to the mapping unit 2 in the preceding stage.

(Embodiment 2) FIG. 4 is a block diagram showing a configuration of a receiving apparatus according to the present embodiment, and receives a signal transmitted by the transmitting apparatus of (Embodiment 1). In FIG. 4, 11 is a receiving antenna, 12 is a band pass filter, 13 is a quadrature demodulator, 15 is an A / D converter, 16 is a guard remover, 17 is a discrete Fourier transform (DFT) unit, 1
Reference numeral 8 denotes a demapping device, and 19 denotes a P / S converter, which perform the same operations as those of the receiving device shown in FIG.

The receiver shown in FIG. 4 has a characteristic of a low-pass filter for removing an image after the quadrature demodulator 13 in the conventional receiver shown in FIG. The band selection amplifier 100, which is a means for increasing the subcarrier power of the other, is arranged.

The operation of the receiving apparatus shown in FIG.
1 receives an electromagnetic wave on a wireless transmission path, removes components outside a desired band with a band-pass filter 12, converts a high-frequency signal into quadrature demodulated by a quadrature demodulator 13, converts the signal into a low-band signal, and a band selection amplifier 100. At the same time as removing image components, amplify the frequency components of subcarriers that are transmitted at low power near the edge of the signal band, and are transmitted at high power near the center of the signal band. The frequency component of the subcarrier is passed through a filter having a frequency characteristic that does not amplify.

The A / D converter 15 converts the analog signal into a digital signal, and the guard remover 16 removes the guard section inserted on the transmission side.
Performs discrete Fourier transform from the in-phase signal and the quadrature signal, performs demapping corresponding to the mapping on the transmission side by the demapper 18, and converts the parallel signal into a serial signal by the P / S converter 19, thereby receiving the signal. Convert to data.

The specific operation of the band selection amplifier 100 will be described below. FIG. 5 is a schematic diagram showing the characteristics of a conventional low-pass filter for image removal, and FIG. 6 is a schematic diagram showing the characteristics of the band selection amplifier 100 used in the present embodiment.
Here, N indicates the number of subcarriers, and fs indicates a subcarrier frequency interval.

Since the signal transmitted from the conventional transmitting device has a spectrum shape as shown in FIG. 2, the low-pass filter of the conventional receiving device simply transmits the signal outside the signal band as shown in FIG. Power is blocked, and in fact, the out-of-band portion has spectral characteristics with a certain slope as shown in FIG. However, in the present embodiment, since the signal having the frequency spectrum shape as shown in FIG. 3 is transmitted on the transmission side, the signal is transmitted with small power at the end of the signal band as shown in FIG. The frequency component of the subcarrier is amplified, and the band selection amplifier 1 having a filter near the center of the signal band and having a frequency characteristic such that the frequency component of the subcarrier transmitted with high power is not amplified.
By arranging 00 and passing a signal having a spectrum as shown in FIG. 3, it is possible to obtain a signal of a uniform level within the band.

By providing means having such a function, it is possible to improve the dynamic range of the A / D converter 15 and the discrete Fourier transformer 17 arranged at the subsequent stage, and change the C / N of each subcarrier. Without this, it is possible to reduce the calculation error caused by the fixed-point calculation.

(Embodiment 3) FIG. 7 is a block diagram showing a part of an input stage of a transmitting apparatus according to the present embodiment. In FIG. 7, reference numeral 20 denotes an importance checker for checking the importance of input data, and reference numeral 21 denotes an importance-considering S / P converter which operates based on the result of the importance checker 20, and is inserted before the mapping unit 2. Is done. The configuration after the mapping unit 2 is shown in FIG.
Is the same as

The operation of the input stage of the transmitting apparatus shown in FIG. 7 is such that the input data and the contents are input to the importance checker 20 to check the importance, and the importance-considered S / P converter 21 determines the level of importance. The signal band of the subcarrier to be transmitted is selected in accordance with, the signal of high importance is transmitted near the center of the signal band of high subcarrier power, and the signal of low importance is at the end of the signal band with low subcarrier power Form the frequency spectrum of the transmitted signal for transmission.

FIG. 8 shows S in the S / P converter 21 considering importance.
FIG. 3 is a schematic diagram showing a relationship between a frequency spectrum and signal importance by / P conversion. As described above, the frequency spectrum of the transmission signal is such that a signal with high importance is transmitted near the center of the signal band with high subcarrier power and a signal with low importance is transmitted at the end of the signal band with low subcarrier power. Is formed.

The receiving side can output a normal received data sequence by performing P / S conversion corresponding to the S / P conversion considering the importance determined on the transmitting side. This importance-consideration S / P conversion means can preliminarily determine the importance information on the transmission side and the reception side, or transmit the information on the S / P conversion method from the transmission side to the reception side. It is also possible to transmit the information and change the information on the importance of the importance-considering S / P conversion means as necessary.

Here, the FEC for correcting the transmission error
When (Forward Error Correction) is performed, it is possible to perform FEC separately for each importance, and it is also possible to perform FEC in consideration of the signal sequence after the importance-considered S / P conversion.

(Embodiment 4) FIG. 9 is a block diagram showing a configuration of a communication device according to the present embodiment. In FIG. 9, 101 is a communication device, 102 is a receiving device, 103 is a transmitting device, and the other reference numerals are the same as those used in FIGS. In the present embodiment, D of receiving apparatus 102
The frequency characteristic of the transmission path obtained by the FT 17 is transmitted to the transmission side, and based on the transmission path frequency characteristic, the transmitting apparatus changes the power of each subcarrier in the power changer 10 and also changes the power according to the importance of the signal. The S / P converter of the importance-considered S / P converter 21 can be changed so that a subcarrier to be transmitted can be selected.

With such a configuration, for example, when the power of a certain subcarrier in the received signal is small due to frequency selective fading or the like, the power of the subcarrier is increased by the power changer 10. At the same time, it is possible to change the importance of the signal by changing the importance of the S / P converter 21 so that the signal of high importance can be transmitted on another subcarrier. A signal corresponding to the degree can be formed.

By forming the transmitting device and the receiving device having the above-described configurations, in this embodiment, a more reliable transmission system that can follow a change in the transmission path can be constructed.

(Embodiment 5) FIG.10 is a block diagram showing a configuration of a transmitting apparatus according to the present embodiment. In FIG. 10, the transmitting apparatus includes a numerically controlled oscillator 22 (NCO: Numerically Controlled Oscillato
r), a power changer 10 that changes the output power of these in-phase and quadrature components, an adder 23 that adds the in-phase component of this output, and an adder 23 ′ that adds the orthogonality component.
It has a symbol timing generator 24. Other symbols are the same as those used in FIGS. 1 to 9.

FIG. 11 is a block diagram showing the configuration of the numerically controlled oscillator 22 of the transmitting apparatus shown in FIG. The numerically controlled oscillator 22 sets an initial phase by the initial phase setting unit 28 based on the output signal of the mapping unit 2 for each symbol timing from the symbol timing generator 24. The accumulator 26 delays the constant phase value ΔΦ25 based on the frequency of each subcarrier by the delay unit 27 and accumulates the same.

After the means for adding the accumulator value to the initial phase set by the initial phase setting device 28, the cutoff device 29 discards the accumulated value in accordance with the address length of the ROM 30 following the subsequent stage. The value of the ROM having the truncated accumulated value as an address is read as an amplitude value. Here, the in-phase and quadrature components are stored in the ROM, and both components are output. Quadrature amplitude modulation (Q
AM) When the amplitude changes as in the
The amplitude is changed by an amplitude changer 31 at the subsequent stage of 30 to cope with this.

Here, if the initial phase 28 based on the output signal of the mapper 2 is set for each symbol timing, a sharp change in the phase occurs, and the spectrum outside the signal band increases. Therefore, the initial phase setting unit 28 does not instantaneously change the initial phase based on the output of the mapping unit 2 but gradually changes the initial phase. Similarly, the amplitude change is also gradually changed by the amplitude changer 31. The initial phase setting unit 28 and the amplitude changing unit 31 operate in synchronization with the symbol timing by a signal from the symbol timing generator 24.

As described above, the out-of-band spectrum can be reduced by gradually changing the phase and the amplitude. Further, since the numerically controlled oscillator is used, the orthogonal condition between subcarriers can be easily and accurately satisfied.

(Embodiment 6) FIG. 12 is a block diagram showing a configuration of a numerically controlled oscillator of a transmitting apparatus according to the present embodiment. In FIG. 12, a numerically controlled oscillator 33 includes a phase step unit 32, an accumulator 26, a delay unit 27, a truncation unit 29, a ROM 30, and an amplitude change unit 31, and includes a mapping unit 2, a symbol timing generator 24
Input signal from.

The phase step unit 32 inside the numerically controlled oscillator 33 gradually reduces the phase step ΔΦ (t) in accordance with the timing from the symbol timing generator 24 in order to mitigate the steep change of the initial phase based on the mapper 2. To change it.

That is, the value of the accumulator 26 is gradually changed to alleviate a steep phase change at each symbol timing. Therefore, the phase step ΔΦ (t) in the phase step unit 32 is not a constant value, but is gradually changed with a change in the initial phase. This change is performed based on a signal from the symbol timing generator 24.

By changing the value of the accumulator 26 as described above, a steep phase change can be reduced, and the out-of-band spectrum can be reduced.

(Embodiment 7) FIG. 13 is a block diagram showing a part around a numerically controlled oscillator of a transmitting apparatus according to the present embodiment. The present invention is characterized by having a variable coefficient setting unit 35 and is configured with a symbol timing generator 24, a numerically controlled oscillator (NCO) 22, a mapping unit 2, and a multiplier 34, thereby achieving the effect of the present invention.

The variable coefficient setting unit 35 gradually increases (or decreases) the value of the variable coefficient by which the complex signal from the NCO 22 is multiplied as a means for providing a ramp section generally used to alleviate the phase discontinuity between symbols. ).

The timing for gradually changing the value of the variable coefficient is synchronized with the signal from the symbol timing generator 24. Then, means for gradually increasing the value of the variable coefficient at the beginning of the symbol section and gradually decreasing the value of the variable coefficient at the end of the symbol section is used.

With such a simple configuration, it is possible to reduce the out-of-band spectrum.

(Embodiment 8) FIG. 14 is a block diagram showing a schematic configuration of a numerically controlled oscillator of a transmitting apparatus according to the present embodiment. In FIG. 14, 31 (, 31 ′, 3
1 ″,...) Are amplitude changers, 35 (, 35 ′, 35 ″,
…) Is an address determination unit, and 36 is a shared RO that is storage means.
M, which corresponds to the numerically controlled oscillator of FIGS.

FIG. 15 is a block diagram showing an example of a specific configuration of the address determination unit 35 in FIG. 14, and the reference numerals are the same as those used in FIG. 11 and FIG.

The shared ROM 36 outputs a value corresponding to the address determined by the address determining section 35. Further, the timing of inputting the address to the shared ROM 36 is time-divided so that no collision occurs between the NCOs.

With such a configuration, a ROM having a large circuit size can be shared between the NCOs, and thus the circuit size can be reduced.

(Embodiment 9) FIG. 16 is a block diagram showing a schematic configuration of a numerically controlled oscillator of a transmitting apparatus according to the present embodiment. In FIG. 16, 31 (, 31 ′, 3
1 ″,...) Are amplitude changers, 35 (, 35 ′, 35 ″,
…) Is an address determination unit, 37 is an input bus, and 38 is a shared R
A storage means 39 having an OM and a control device, and 39 is an output bus, which corresponds to the numerically controlled oscillator shown in FIGS.

The storage means 38 outputs a value corresponding to the address value from the input bus 37 to the output bus 39. Specifically, the input bus 37 is connected to each address determination unit 35, 3
The address value time-divided between 5 ', 35 "... Is input, and the control device inputs a signal bundle from the input bus 37, extracts a corresponding value from the shared ROM, performs parallel processing, and outputs the corresponding value to the output bus 39. The output is configured so that addresses do not collide.

With such a configuration, the shared ROM, which is a shared lookup table, can be used efficiently, and the circuit can be easily designed.

(Embodiment 10) FIG.17 is a block diagram showing a schematic configuration of a numerically controlled oscillator of a transmitting apparatus according to the present embodiment. In FIG. 17, 31 (, 31 ′, 3
1 ″,...) Are amplitude changers, 35 (, 35 ′, 35 ″,
..) Is an address determination unit, 36 is a shared ROM, 40 is an address match detector, and 41 is an address shifter.
1 and the numerically controlled oscillator of FIG.

In the present embodiment, each address value determined by the address determination unit 35 is
In step S1, the addresses are shifted by a fixed value in the address shifter 41 at random or in accordance with a certain rule.

By adjusting the address in this manner, the shared ROM 36 can be used efficiently.
The address coincidence detector 40 and the address shifter 41 simultaneously store the same address value in the shared ROM 36.
, The ROM can simultaneously output a value corresponding to the input address value.

Although FIG. 17 shows a case in which the shared ROM 36 is used, the present invention can be similarly carried out in the case of using the storage means described in the ninth embodiment.

[0077]

As described above, according to the present invention, OFDM
In the transmission apparatus and the reception apparatus using the transmission method, the spectrum outside the signal band can be reduced by a simple method, and the advantageous effect that the frequency can be effectively used can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a transmission device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a frequency spectrum of an input signal of a power converter according to an embodiment of the present invention;

FIG. 3 is a schematic diagram showing a frequency spectrum of an output signal of the power converter according to one embodiment of the present invention;

FIG. 4 is a block diagram showing a configuration of a receiving device according to an embodiment of the present invention.

FIG. 5 is a schematic diagram showing a frequency spectrum characteristic of a conventional low-pass filter for image removal.

FIG. 6 is a schematic diagram showing a frequency spectrum characteristic of the band selective amplifier according to one embodiment of the present invention;

FIG. 7 is a block diagram showing a configuration of a part of an input stage of the transmission device according to one embodiment of the present invention;

FIG. 8 is an S / P considering importance according to an embodiment of the present invention.
Schematic diagram showing the relationship between frequency spectrum and signal importance by S / P conversion in a converter

FIG. 9 is a block diagram showing a configuration of a communication device according to one embodiment of the present invention;

FIG. 10 is a block diagram showing a configuration of a transmission device according to an embodiment of the present invention.

FIG. 11 is a block diagram showing a configuration of a numerically controlled oscillator in a transmission device according to one embodiment of the present invention.

FIG. 12 is a block diagram showing a configuration of a numerically controlled oscillator in a transmission device according to one embodiment of the present invention.

FIG. 13 is a block diagram showing a partial configuration around a numerically controlled oscillator in a transmission device according to an embodiment of the present invention;

FIG. 14 is a block diagram showing a schematic configuration of a numerically controlled oscillator of the transmission device according to one embodiment of the present invention;

FIG. 15 is a block diagram showing a configuration of an address determination unit in the numerically controlled oscillator according to one embodiment of the present invention.

FIG. 16 is a block diagram showing a schematic configuration of a numerically controlled oscillator of the transmission device according to one embodiment of the present invention;

FIG. 17 is a block diagram showing a schematic configuration of a numerically controlled oscillator of the transmission device according to one embodiment of the present invention;

FIG. 18 is a block diagram showing a configuration of a transmission device and a reception device according to a conventional OFDM method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 S / P (serial / parallel) converter 2 mapping device 3 IDFT (inverse discrete Fourier transform) device 4 guard inserter 5 quadrature modulator 6 band-pass filter 7 up-converter 8 low-pass filter 9 transmission antenna 10 power changer Reference Signs List 11 receiving antenna 12 band-pass filter 13 quadrature demodulator 14 low-pass filter 15 A / D (analog / digital) converter 16 guard remover 17 DFT (discrete Fourier transform) unit 18 demapper 19 P / S (parallel / parallel / Serial) converter 20 Importance checker 21 Importance consideration S / P converter 22 Numerically controlled oscillator (NCO) 23 Adder 24 Symbol timing generator 25 Constant phase output device 26 Accumulator 27 Delay device 28 Initial phase generator 29 Truncation Instrument 30 ROM 31 Amplitude changer 32 Variable Phase step generator 33 Numerically controlled oscillator (NCO) 34 Multiplier 35 Variable coefficient setting device 36 Shared ROM 37 Input bus 38 Storage means 39 Output bus 40 Address coincidence detector 41 Address shifter 100 Band selection amplifier 101 Communication device 102 Receiving device 103 transmitting device

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kentoku Kunieda 3-10-1 Higashi-Mita, Tama-ku, Kawasaki-shi, Kanagawa F-term in Matsushita Giken Co., Ltd. (Reference) 5K022 DD01 DD13 DD19 DD23 DD33

Claims (14)

[Claims] In a communication system using an orthogonal frequency division multiplexing (OFDM) transmission system in which each subcarrier is modulated, in a region separated from a center frequency by a certain frequency width or more in a signal band, the subcarrier power is set to the center. An orthogonal frequency division multiplexing transmission system using a communication signal whose frequency spectrum shape is formed so as to have a gradient that gradually decreases as the frequency increases. 2. The apparatus according to claim 1, further comprising power changing means for gradually decreasing the subcarrier power in a region apart from the center frequency by a certain frequency width or more in the signal band as the distance from the center frequency increases. A transmission device using an orthogonal frequency division multiplex transmission system. 3. A filter function for gradually increasing the subcarrier power in a region apart from the center frequency by a certain frequency width or more within the signal band as the distance from the center frequency increases, and removing a signal in a frequency region outside the signal band. 2. A receiving apparatus using an orthogonal frequency division multiplexing transmission method according to claim 1, further comprising a band selection amplification means having the following. 4. The orthogonal frequency division multiplexing transmission system according to claim 1, wherein the communication signal is formed by subcarriers selected according to importance. 5. The communication signal according to claim 4, wherein the sub-carriers determined to be less important are arranged in a frequency spectrum region farther from the center frequency.
Orthogonal frequency division multiplex transmission system as described. 6. The orthogonal frequency division multiplex transmission system according to claim 4, wherein the communication signal includes transmission line frequency characteristic information. 7. An importance investigating means for inputting transmission data and content information, judging importance of each subcarrier and outputting importance information using the orthogonal frequency division multiplexing transmission method according to claim 4 or 5. And importance consideration S / P conversion means for inputting the transmission data and the importance information, selecting a subcarrier based on the importance information, and performing serial / parallel (S / P) conversion. The transmitting device according to claim 2, wherein: 8. An importance investigating means for inputting transmission data and content information, judging importance of each subcarrier and outputting importance information, using the orthogonal frequency division multiplexing transmission method according to claim 6, The transmission data, the importance information, and the transmission path frequency characteristic information are input, and a subcarrier is selected based on the importance information and the transmission path frequency characteristic information to perform serial / parallel (S / P) conversion. 3. The transmission apparatus according to claim 2, further comprising S / P conversion means for performing importance, wherein a power changer changes the subcarrier power based on the transmission line frequency characteristic information. 9. A numerically controlled oscillator (NCO) for inputting a timing signal and a subcarrier and outputting in-phase component and quadrature component subcarrier power according to the subcarrier is provided for each of the number of subcarriers. A power changer that changes the power value of the component subcarrier power, a first adder that adds the power value of the changed in-phase component, and a second adder that adds the power value of the changed quadrature component, The transmitting apparatus according to claim 2, further comprising: a quadrature modulator that receives an output of the first adder and an output of the second adder and performs quadrature modulation. 10. A numerically controlled oscillator includes a phase step generator for outputting a phase step value such that the phase changes gradually and continuously in time, and an accumulator for adding the phase step value. The transmitting device according to claim 9, wherein: 11. A variable coefficient setting device for generating a variable coefficient based on a timing signal, and a multiplier for multiplying the output of the numerically controlled oscillator by the variable coefficient, wherein a change in amplitude is gradually amplified or reduced in time. The transmitting device according to claim 9, wherein the variable coefficient setting device is controlled so as to attenuate. 12. A numerically controlled oscillator for determining an address value corresponding to a subcarrier and selecting and outputting a value based on the address value shared by all numerically controlled oscillators corresponding to the number of subcarriers. The transmission device according to claim 9, further comprising a storage unit that performs the operation. 13. A numerically controlled oscillator comprising: an address determining means for determining an address value corresponding to a subcarrier; and a numerically controlled oscillator which is shared by all of the numerically controlled oscillators corresponding to the number of subcarriers and receives and matches all address values. Address match detecting means for judging whether or not there is a match, and outputting a judgment value; if the judgment value includes match information, shift the address value by a necessary amount and output; if there is no match information, output the address value as it is 12. The transmitting apparatus according to claim 9, further comprising: an address shift unit; and a storage unit that selects and outputs a value based on an address value from the address shift unit. 14. A storage means for storing an output value associated with an input, and a control means for inputting all address values, extracting corresponding values from the ROM based on each of the address values, and outputting the values in parallel. 14. The transmitting device according to claim 12, wherein the transmitting device comprises: